(1) Field of the Invention
The present invention relates to a fixing device and the like for fixing an unfixed toner image on recording paper that is conveyed by an endless belt for conveying recording paper, by fusing the toner by irradiation of laser light.
(2) Description of the Prior Art
Image forming apparatuses (e.g., printers, etc.) using electrophotography include a fixing device that thermally fuses the toner image formed on the paper to fix the toner image to the paper. As one example of the fixing device, a fixing device of a paired roller type made up of a fixing roller and a pressing roller has been known, as disclosed in patent document 1 (Japanese Patent Application Laid-open H11-038802).
The fixing roller is a roller member formed of a hollowed metal core made of aluminum or the like and an elastic layer formed on the surface thereof with a halogen lamp as a heater arranged inside the metal core. With this arrangement, a temperature controller makes on/off control of the halogen lamp in accordance with the signal output from a temperature sensor provided on the fixing roller surface so as to control the temperature on the fixing roller surface.
The pressing roller is a roller member made of a metal core and a heat-resistant elastic layer of silicone rubber etc., provided as a coating layer on the metal core. This pressing roller is put in press-contact with the peripheral side of the fixing roller so that the elastic layer of the pressing roller is elastically deformed forming a nip area between the fixing roller and the pressing roller.
In the fixing device having the above configuration, the paper with an unfixed toner image formed thereon is fed into the nip area between the fixing roller and the pressing roller and conveyed by rotating these two rollers while the toner image on the paper is fused by heat from the fixing roller surface and fixed to the paper.
However, in the conventional paired roller type configuration, since the fixing roller and the pressing roller should be put under a room temperature condition when the machine is activated first in the morning, the fixing device needs time to warm up to increase its temperature to the predetermined temperature from when the machine is activated. Further, in the waiting mode when no copying operation is performed, it is necessary to keep the roller surface at a predetermined temperature, hence heat the roller continuously even when no copying operation is performed. In this way, waste energy is consumed other than copying operations.
To deal with this, a method of fixing toner in an efficient manner without consumption of waste energy has been proposed in patent document 2 (Japanese Patent Application Laid-open 2005-55516) in which a fixing device fixes toner using laser power.
According to patent document 2, a plurality of low-power semiconductor lasers are used so that individual laser light rays emitted from the multiple laser light sources are focused and superimposed on the same area of the toner image, to thereby fuse and fix toner by making up for shortage of power. This disclosure asserts that this configuration enables use of low-power inexpensive semiconductor lasers, hence can make the whole apparatus simple.
However, the above-described technology is effective in fixing unfixed toner images in a fair condition, but has the problem that the laser light from the fixing device is emitted wrong so that intensive laser light is radiated on and heats the recording paper conveyor, damaging the recording paper conveyor.